L9: signed integers for DVM-BASIC — Int type, negative literals

[liqdmetal]

Summary

L9 from the DVM-BASIC language agenda (P2): signed 64-bit integers — DIM i AS Int, negative literals, signed arithmetic and comparisons, Int function parameters and returns. Ends the two's-complement tricks contracts currently use for delta accounting.

The syntax

DIM balance AS Int
DIM fee AS Int
LET balance = 100
LET fee = -30
LET balance = balance + fee      ' 70
IF balance - 100 == -30 THEN ... ' signed comparison
Function Diff(a Int, b Int) Int  ' negative returns
    RETURN a - b
End Function

Implementation

• Int = Vtype 0x7, stored in ValueInt64 (Go int64)
• Negative literals: UnaryExpr{SUB} handled in the evaluator
• Signed arithmetic: evalBinaryExpr gains an int64 path (ADD/SUB/MUL/QUO/REM + all comparisons); int64-vs-uint64 mixed operands reinterpret two's-complement so IntVar == 70 works naturally
• Every type-switch site extended (DIM, LET, arrays, params, returns, CONST resolution)
• Consensus-neutral: Locals-only — contracts can't STORE an Int (STORE takes the uint64 scalar path), so serialized SC state is untouched
• Gated >= 10.0.0 like the rest of the L-series

Tests (dvm/control_flow_l9_test.go, 4 cases)

Test	Verifies
TestL9_IntBasics	signed delta: 100 + (−30) = 70, balance−100 == −30
TestL9_NegativeLiteral	−5, −x, x·−1
TestL9_IntParam	Int param, negative return
TestL9_VersionGate	Int at 1.2.3 rejected

Full dvm suite green (33 control-flow tests).

Relationship

• Stacks on L6 (PR L6: Bool type for DVM-BASIC (fixes #114, stacks on #111) #115) — same type-system extension pattern
• L-series now 8/10 delivered (L1–L4, L6–L9); remaining: L5 (multi-value returns) and L10 (block scoping), both structural

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Branch: feature/dvm-l9-int in the fork liqdmetal/derohe-improvements-by-liqdmetal (stacked on feature/dvm-l6-bool).